Architectural Precast Elements:

Designing for the Unknown

A Phoenix "hotel" for high-tech switching equipment makes a precast box into a one-of-a-kind building — built without people in mind

Tenants have been repeatedly inquiring about the progress of a four-story architectural and structural precast concrete building with no windows and meager parking that's going up in downtown Phoenix. But by its completion in June 2001, the Phoenix developer, Cole Cos. expects tenants to flock to it.

The 135,160-square-foot building is not pre-leased because the high-tech companies who would use it to house their electronic switching and routing equipment want to lease space in the first available space to meet their needs - needs that keep changing. "They're in a mad dash to capture market share," says Trent Rustan, vice president at Cole Cos. The tenants of this "carrier or switch hotel" could be companies such as Qwest, local Bell competitors and Internet service providers.

Precast Saves Time, Money
The speed-to-market component of the building drove the schedule, which in turn affected the building material choice. Early cost analysis showed that using architectural and structural precast concrete instead of steel and precast would save 17 percent of costs and one month in the construction schedule, explains general contractor Glenn Leier, senior project manager and vice president at Wespac Construction Inc. in Phoenix. "It became a no-brainer to use precast."

Another advantage to using precast concrete is its inherent inorganic composition, which provides a natural fire resistance. No additional fireproofing material needed to be added to meet the required fire ratings. This also means that tenants don't have to worry about such fireproofing materials deteriorating a few years from now and flaking into the intricate electronic equipment, points out Jack Gill, senior project consultant at Coreslab Structures (ARIZ) Inc. in Phoenix.

Precast also provides greater floor-to-floor height than steel buildings of the same overall height. SwitchX's floor-to-floor height is 17 feet, making the clear height in excess of 12'6", which easily permits rack heights of 7 to 8 feet as well as space for overhead fiber lines, cables and HVAC system conduit. Most traditional office buildings have a clear height of only 8 to 9 feet.

In addition, the many racks of switches and routers require vast amounts of cooling and a redundant power system so the tenants' equipment never goes down. This can be critical for tenants, for if popular sites go down for even as little as 45 minutes, they can lose millions of dollars. An incredible floor capacity is needed to support the batteries that will be housed on each of the building's four floors - batteries that can add up to 300 pounds per square foot of live load.

Heavy Loading Provided
"The heavy floor-loading ability in the SwitchX facility gives tenants the flexibility to lay out their space any way they want," says Jeffrey Maas, project manager for Patrick Hayes Architecture in Scottsdale, Ariz. In addition to the batteries, which are the first line of power should electricity fail, generators at street level in their own screened yard on the north side of the building kick in if the batteries fail.

With the equipment having three to four times the load required in most office buildings, "Concrete was the logical choice," says Patrick Hayes, principal in the architectural firm. "Concrete lends itself to better security as well." The floor load capacity is 10 times that needed for a normal passenger car parking structure (after 50 psf live load is reduced to 30 psf), Coreslab's Gill says.

This building is likely the first of its kind, Rustan notes, as most such switching stations are in retrofitted buildings. "A typical retrofit might cost as much as $200 per square foot without the many special features we are including," he says. For high-rise buildings being retrofitted as switch hotels, designers might have to determine where to put the backup generators for the 15th floor tenant. And since 75 to 100 pounds per square foot is a typical load for most office buildings, a retrofit would need a superstructure to shore up the building.

To gain a competitive advantage, the SwitchX building was built so it will be easy to upgrade due to its open spaces, load-bearing capability and pre-negotiated power arrangements with the utility company. "What was just imagined yesterday is now happening," Rustan says. "Tenants' power requirements are already almost off the charts. So SwitchX was designed for future flexibility. We won't be obsolete."

The SwitchX substructure was designed to use caissons with grade beams to transfer the vertical and horizontal forces from the structure into the bearing soils. "The building is really just a structural box capable of supporting large live loads over the long spans used in the design of the building," says Fred Noelke, principal in charge of the project at Paul-Koehler Consulting Structural Engineers Inc., in Scottsdale, Ariz. "It's like a bunker that's built to last a lifetime with the versatility to be used with many different usage changes. Using a precast concrete structure, you know you are constructing a building of high quality."

Originally the design called for steel columns but as the building quickly became a full precast system after cost and schedule analysis, the 10 - by 10 - inch steel columns became 2 - by 2-foot precast columns. To ensure no loss of floor space, the 30 - by 30-foot bays were changed to 42 - by 26 - foot bays so fewer columns were needed. Converting to precast columns shaved four weeks from the schedule, Maas says. "That time savings was critical in telecommunications - it's more valuable than cost savings."

Early in the design phase, the building team held several meetings with the local planning committee. At first, the committee wanted glass on the windowless building so it would look like the surrounding office and apartment high-rises. "Our hearts sank," Maas says. "We wanted to be true to the building system."

The architect used its computerized animation system to show the committee three-dimensional flyby video renderings. This allowed the committee to view what the building would look like in place, and suddenly the building's lack of windows no longer mattered. "We never would have gotten the design past the committee without the renderings," Hayes says. To avoid a big-box look, the architect added cast-in reveals and sand-blasted color banding to add depth to the design.

Precaster Brought In Early
Wespac brought precaster Coreslab on board about four months prior to having full construction documents readied, and its crews began casting pieces before final approval was received from Phoenix officials. "We were at risk for some code issues," Maas says. "But we felt certain we could adjust to any concerns that arose."

For example, the building team was able to show the number of required parking spaces could be reduced (to 150 car spaces or so) because the building would have a small number of people in it at any one time. Normally, office buildings require up to six spaces per 1,000 square feet of floor space, but this building has only one-half space per thousand. Because this building represents a new genre, the director of planning for Phoenix granted a variance and is now in the process of changing the ordinances to accommodate it and other buildings in the future.

"Phoenix was surprisingly receptive," Hayes says. Having switch hotels is a big selling point for a city because they encourage high-tech companies to set up shop. Rustan says that the market is deep in Phoenix. The building is adjacent to a fiber-optic network of nine providers and a primary Qwest switching tandem.

Delivery of the 540 truckloads of precast concrete began November 15, with erection taking only 10 weeks. It concluded January 31, 2001. The floors feature 32-inch-deep double tees that will have a 4-inch-thick concrete topping, while the roof consists of 24-inch-deep double tees with four inches of insulation.

The north and south exterior walls include 8-inch-thick curtain walls, and the east and west walls are load-bearing, 10-inch-thick walls. The walls measured 150 to 200 feet wide and 84 feet high. To create that height, the precaster stacked three wall panels with mitered corners and added a 16-foot parapet that blocks a view of the roof with its extensive air-cooling systems.

The precast components in the $8.5-million construction project came to $2.4 million. "Building the structure itself was not a challenge," Leier says. "It's an erector set." All the connection points have standard welds.

HVAC Shafts Outside
Each tenant will have its own air-conditioning system on the roof with condensate lines running into the building via exterior utility shafts. Two 6,000-pound service elevators at the north end of the building have extra-high cabs that go all the way to the roof. The building's columns extend four feet through the double-tee roof deck and are topped by a metal grill on which the air handling equipment sits. Normally this type of equipment sits directly on the roof and penetrates it. SwitchX's grillwork design permits future roof repairs to occur without shutting down any systems.

The electronic systems SwitchX will house will require huge amounts of conduit. And each tenant wants its own lines. "No one wants to share, so I pulled the utility shaft from the middle," Hayes says. By putting the utility shaft on the outside of the building, the architect could treat it as an architectural element. The exterior shaft is about 30 feet wide and is as tall as the building. It is made from curved, perforated metal panels that are further broken down into four equal smaller shafts within it to keep each tenants' cables separate and dedicated. Spandrel panels pop out at each floor level around the outside of the four exterior utility shafts as a design element and allow exterior servicing of wires.

The challenge is anticipating what the tenants will want and how to route the power and conduit. The utility shaft space availability is based on square footage leased by the tenants. The shafts are empty until filled by the tenants. Power access is a huge concern because the need for it keeps growing in the tech industry. The developer worked closely with local power companies to be assured the electricity could be supplied to the building by the substations. At one point in the original design, the developer even considered building an electrical substation on site, but that was dropped to maximize building size.

Phase II Readied

Phase II of the project, which likely will begin within a year and add 137,440 square feet to the building, will expand the structure on the west side to make the whole project appear as one unit. The building is designed for full expansion because of the open spaces. The service entry section is designed for in excess of 100 watts per square foot, which is 10 to 20 times what most office buildings need. Each of the two construction phases is designed for six 3,000-amp services. Cole Cos. is currently designing a similar type of building in Las Vegas that should be complete by the end of 2001. Numerous other cities are also in the design stage.

"The most difficult part of the project is working with the unknown," Maas says. "That is, figuring out a design for tenants when you don't know their individual needs. The second hardest part is keeping up with a technology that keeps changing." The schedule has been grueling, but the builders and designers all express a thrill in building such a unique type of building. "It's like running a marathon," Hayes says. "There's nothing but glory in the end."